1. Field of Invention
This invention relates generally to transformers for transferring electrical energy from a primary winding to a secondary winding, and more particularly to an iron-free transformer in which the transfer of energy is effected without any electrical connection or inductive coupling between the windings.
2. Status of Prior Art
A conventional transformer, whether a power transformer, an audio or radio frequency transformer, a modulation transformer or any other known type, functions to transfer energy from an input circuit or primary winding to an output circuit or secondary winding, by means of magnetic induction. The transfer of energy is effected by magnetic linkage between the circuits.
The principle underlying the operation of a conventional transformer is Faraday's law, which states that when the magnetic flux enclosed within a circuit varies, then induced in the circuit is an electrical current proportional to the rate of variation.
In its most elementary form, a conventional transformer consists of two coils wound of copper wire and inductively coupled to each other. When an alternating current of a given frequency flows in either coil, an electromagnetic force (emf) is induced in the other coil. The coil connected to an alternating current source is the primary winding of the transformer, and the emf produced across this winding is the primary emf. The emf induced in the other coil, which is the secondary winding, may be greater or less than the primary emf, depending on the ratio of primary to secondary turns which determine whether the transformer is a step-up or a step-down transformer.
Many transformers are provided with a stationary core of an iron alloy about which the primary and secondary windings are wound. Because of the high permeability of iron alloys or other ferromagnetic materials, most of the magnetic flux is concentrated in the core, and tight inductive coupling is thereby effected between the windings. Hence, the primary and secondary emf's bear almost exactly the same ratio to each other as the turns in the primary and secondary windings.
A conventional iron-core transformer has a high degree of efficiency, for the only losses encountered in transferring electrical energy are due to eddy currents set up in the iron core and heat generated as a result of the resistance of the copper windings.
There are some situations which require the transfer of energy, yet the use of an iron-core transformer for this purpose is not acceptable. Thus, one cannot use an iron-core transformer in the environment of a particle accelerator, for the intense, steady state magnetic fields which are produced in the accelerator will saturate an iron core and render the transformer inoperative. And there are other situations in which losses due to eddy currents induced in the iron core and heat produced by the resistance of the windings cannot be tolerated.
Thus in radio astronomy in which extremely weak radio signals originating in outer space are intercepted by an antenna and conveyed to a preamplifier, in order to prevent these signals from being buried in noise, it is the practice to convey the signals picked up by the antenna to the preamplifier by means of superconductive wires. These are maintained at a cryogenic temperature, that of liquid helium or liquid nitrogen, depending on the nature of the superconductor. In this context, one cannot step up the signal conveyed by the superconductive wires by means of a conventional transformer, for the losses encountered in such transformers will worsen the existing signal-to-noise ratio.